Whenever a patient requires total respiratory support, he is connected to a positive pressure volume ventilating pump by means of a closed breathing circuit. A plastic or rubber tube, called an endotracheal tube, is inserted through the patient's mouth into his trachea to supply a prescribed volume of oxygen-containing gas from the volume ventilating pump. Near the end of the tube inserted into the trachea is a plastic balloon called a "cuff" which encircles the outside diameter of the tube. This cuff is inflated by means of a line bonded to or incorporated into the wall along the length of the tube. The cuff, when inflated, separates the upper airway or trachea from the closed breathing circuit. This allows precise delivery of a prescribed volume of oxygen-containing gas to the patient and prevents the aspiration of oral and/or gastric material into the trachea.
However, because the cuff must be constantly kept inflated, the amount of pressure it exerts on the delicate tracheal tissue becomes a critical factor. If the pressure is excessive, it prevents or restricts the flow of blood to the tracheal tissues and can cause necrosis (death) or serious damage to the tissue. This damage can lead to many immediate and long term medical problems.
For the reasons given above, it is advantageous to inflate the cuff to completely close off the trachea during delivery of the prescribed volume of gas (inspiration) and deflate the cuff to a minimum pressure during exhalation of the gas (expiration). The deflation of the cuff leaves just the minimum amount of pressure to prevent entrance of foreign bodies or aspiration into the trachea. These previous systems are directed towards management of the patient's airway and minimizing the cuff pressure during expiration. One of the forerunners of these systems utilizes a syringe to provide a prescribed volume of air to the cuff during inspiration and releases that volume of air during expiration. In this system, a nebulizer drive line is used to drive the syringe to provide a prescribed volume of air to the cuff. In other words, the volume of the syringe is pumped into and then released from the cuff cyclically. No attempt to regulate the cuff pressure in the exhalation cycle is attempted with this system. Various other systems use complicated valving mechanisms, but they are not generally synchronized with the operation of the volume ventilating pump. For this reason, none of the techniques now known or in use are totally satisfactory. They are either time consuming, hazardous to the patient or both and are, in any case, generally circumvented by poorly trained, overworked or inattentive staff members. The necessity of providing a good airway seal is paramount, regardless of the cuff pressure.
Therefore, it is one object of the present invention to provide a endotracheal tube cuff inflation and deflation control system which is synchronized with the volume ventilating pump.
Another object of the present invention is to provide an endotracheal tube cuff inflation and deflation system in which the maximum and minimum pressures are precisely regulated.
Still another object of the present invention is to provide a system for inflation and deflation of an endotracheal tube cuff which utilizes an exhalation valve pilot line.
Yet another object of the present invention is to provide a system for controlling inflation and deflation of an endotracheal tube cuff which provides a positive cutoff for maximum and minimum pressure of inflation of the cuff.